Much work has been done over the years to convert heavy hydrocarbonaceous materials to more valuable lighter boiling products. One such process is an integrated fluid coking-gasification process in which a heavy hydrocarbonaceous chargestock is fed to a coking zone comprised of a fluidized bed of hot solid particles, usually coke particles, sometimes referred to as seed coke. The heavy hydrocarbonaceous material is reacted in the coking zone resulting in conversion products which include a vapor fraction and coke. The coke is deposited on the surface of the seed particles. A portion of the coked-seed particles is sent to a heater which is maintained at a temperature higher than that of the coking zone where some of the coke is burned off. Hot seed particles from the heater are returned to the coking zone as regenerated seed material which serves as the primary heat source for the coking zone. Coke from the heating zone is circulated to and from a gasification zone which is maintained at a temperature greater than the heating zone. In the gasifier, substantially all of the coke which was laid-down on the seed material in the coking zone, and which was not already burned-off in the heating zone, is burned, or gasified, off. Some U.S. patents which teach an integrated fluid coking-gasification process are U.S. Pat. Nos. 3,726,791; 4,203,759; 4,213,848; and 4,269,696; all of which are incorporated herein by reference.
Myriad process modifications have been made over the years in fluid coking in an attempt to achieve higher liquid yields. For example, U.S. Pat. No. 4,378,288 discloses a method for increasing coker distillate yield in a thermal coking process by adding small amounts of a free radical inhibitor.
Also, U.S. Pat. No. 4,642,175 discloses a method for reducing the coking tendency of heavy hydrocarbon feedstocks in a non-hydrogenative catalytic cracking process by treating the feedstock with a free radical-removing catalyst so as to reduce the free radical concentration of the feedstock.
A problem which is being increasingly encountered is slagging in the gasifier of an integrated fluid coking-gasification commercial unit. Slagging is a complex phenomenon which is influenced by many factors and which can be a cause of major operability problems. For example, the formation of significant amounts of slag can cause blockage of the grid assembly in the gasifier. The grid assembly is comprised of inlet pipes for the introduction of steam and the oxygen-containing gas, and it is located at the bottom of the gasifier. Blockage of this grid assembly will increase the pressure and have an adverse effect on the flow distribution in the bed. If the blockage becomes excessive, design gasification rates may not be achievable and/or run lengths may have to be reduced. Slags can also corrode the cap materials of the grid assembly and form even larger slag accumulations. It is believed that the presence and build-up of vanadium salts in the gasifier are the chief cause of slagging. Consequently, there exist a need in the art for ways to mitigate slagging problems.